Hi rukhvagif,
I found a few sources on the Internet about importing to the EU & Germany, listed below. I suspect there are more but I am restricted to English-language sites only.
German Business Portal
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Information on EU Import Duties
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I strongly suggest giving your local business centre a call as well as Customs. They will be able to answer specific questions you have.
In general, within EU there are no customs, duties, payments, extra taxes, import problems. The whole point of the EU is to make trade between these countries super easy. It's a great idea to sell on more than one eBay site as you can take advantage of the opportunities different markets provide.
The eBay Germany seller area will also have some useful advice:
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One thing to note: Apparently when you sell on eBay Germany you must have a returns policy on your listings. You are legally obliged to do this and I understand eBay Germany have a recommended wording on the site.
Hope that helps